Support external statemanager in VM constructor

lib/index.js

@@ -28,21 +28,27 @@ VM.deps = {
 /**
  * @constructor
  * @param {Object} [opts]
- * @param {Trie} [opts.state] A merkle-patricia-tree instance for the state tree
- * @param {Blockchain} [opts.blockchain] A blockchain object for storing/retrieving blocks
+ * @param {StateManager} [opts.stateManager] A state manager instance
+ * @param {Trie} [opts.state] A merkle-patricia-tree instance for the state tree (ignored if stateManager is passed)
+ * @param {Blockchain} [opts.blockchain] A blockchain object for storing/retrieving blocks (ignored if stateManager is passed)
  * @param {Boolean} [opts.activatePrecompiles] Create entries in the state tree for the precompiled contracts
  */
 function VM (opts = {}) {
-  this.stateManager = new StateManager({
-    trie: opts.state,
-    blockchain: opts.blockchain
-  })
+  this.opts = opts
+
+  if (opts.stateManager) {
+    this.stateManager = opts.stateManager
+  } else {
+    this.stateManager = new StateManager({
+      trie: opts.state,
+      blockchain: opts.blockchain
+    })
+  }
 
   // temporary
   // this is here for a gradual transition to StateManager
   this.blockchain = this.stateManager.blockchain
   this.trie = this.stateManager.trie
-  this.opts = opts || {}
 
   // precompiled contracts
   this._precompiled = {}